The evidence that plasminogen, the focus of this application, plays an essential role in fibrinolysis, is indisputable but other functions have been more recently ascribed to the molecule. Most prominent among these is the involvement of plasminogen in cell migration. The arena in which this latter role becomes particularly evident is in inflammatory cell recruitment. Thus, studies in plasminogen-deficient mice have shown blunted leukocyte recruitment in thioglycollate-induced peritonitis, atherosclerosis, restenosis, arthritis, asthma and angiogenesis, all examples of specialized inflammatory responses. The role of plasminogen in leukocyte migration depends upon its interactions with binding sites on cell surfaces. These binding sites are heterogenous, but accumulated data now have narrowed down the number to five plasminogen receptors that may be key to its interaction with leukocytes. Aim 1 will analyze the role of these five candidate plasminogen receptors utilizing in vitro and in vivo analyses in mice to assess the contribution of each in different inflammatory responses. Plasminogen contains two classes of sites that are critical to its biological functions: its lysine binding sites (LBS), which are associated with its kringles and mediate its interactions with cell surfaces, and its active site, which is associated with its light chain and catalyzes its proteolytic functions. In Aim 2, reconstitution approaches by administration of purified proteins into Plg-/- mice and by transgenesis into these animals will be undertaken to dissect the contributions of the LBS and the active site in different inflammatory responses in vivo. In addition, modulators of the LBS of plasminogen, apoprotein(a) and TAFI, occur naturally and their influence on plasminogen-dependent inflammatory responses of plasminogen will be evaluated. The possibility that the interaction of plasminogen with its receptors leads to intracellular signaling events and downstream consequences has not been assessed in leukocytes. Based on preliminary data showing that signaling events are induced by plasminogen, the third aim of this proposal will analyze the signaling pathways evoked, the consequences of such signaling and the plasminogen receptors involved in transducing these signals. Overall, these studies will provide new insights into the functions of plasminogen and will lead to a greater understanding of the molecular and cellular events that regulate its contribution to inflammatory responses.